The long-term goals reflected in this proposal have not changed: 1) to determine the manner in which muscles and populations of fibers within muscles are recruited during locomotion; and 2) to investigate the relationship between muscular activity and muscular metabolism. Miniature swine, which are increasingly recognized as the best non-primate models for human cardiovascular physiology, will be used to make simultaneous measurements of skeletal muscle activity (EMG and glycogen depletion), circulation (muscle blood flow and capillary transit time), and metabolism (individual muscle VO2 and net lactate release) during treadmill locomotion up to the speed that elicits maximum O2 consumption. This will represent the first time that these critical measures have been made at the same time in the same animal (or human subject), and will permit direct quantitation of the interrelationships among the variables in muscles of differing fiber type composition and function. These measurements will allow determination of limitations to aerobic power imposed by O2 delivery and uptake in individual muscles. The specific objectives of these studies will be to directly quantitate muscle activity, muscle O2 delivery, and muscle metabolism during locomotion as a function of exercise intensity to VO2max which the relationships among the 3 variables have been physiologically altered. The relationships among the variables will be physiologically altered in 2 ways. In the first, the animals will undergo a prolonged treadmill training program designed to increase aerobic power. In the second, alterations in the fiber recruitment, circulatory, and metabolic patterns will be measured during prolonged submaximal exercise with and without evaporative cooling of the animals. The findings from these proposed studies will significantly increase understanding of the mechanisms underlying cardiovascular and metabolic responses of individual skeletal muscles of differing fiber type composition to exercise in conscious animals. These relationships have previously been determined only at the "whole-body" level or in isolated muscle.